Like the human, rabbit relaxin (RXN) has been isolated from both ovarian and placental tissue. It has been suggested that human placental RXN is of ovarian origin. The main objective is to establish the rabbit as a model for studying the origin and release of this hormone (especially that found in the placenta). Radioimmunoassay will be used to determine 1) the normal pattern of rabbit serum RXN levels throughout pregnancy parturition and lactation; 2) the serum RXN levels during pregnancy and parturition in the ovariectomized, progesterone treated rabbit; 3) the serum RXN levels in intact pregnant rabbits in which the fetal numbers are varied by fetectomy; 4) the serum RXN levels in intact pregnant rabbits in which the conceptus (fetal and placental unit) number is surgically varied. This should provide information concerning the influence of the fetus and/or placenta on RXN levels. The ovarian and placental RXN will be purified by gel filtration and ion exchange chromatography and compared as to biochemical properties such as: 1) isoelectric point as determined by column isoelectric focusing; 2) molecular weight as determined by SDS gel electrophoresis. This procedure will also be used with reducing conditions to evaluate interchain disulfide interactions; 3) glycoprotein staining procedures for use in acrylamide gels will be used to determine if such a complex is reponsible for the high molecular weight (30,000 Daltons) rabbit RXN isolated in our preliminary studies; 4) amino acid analysis. The above information should indicate whether the relaxins isolated from the different tissues are similar. The yield of RXN from the rabbit is greater than the human tissue, therefore, making the rabbit a good model for studying the ovarian and placental hormone. The cellular organelles responsible for storage of RXN will also be determined using electron microscopy immunocytochemistry. Ovarian, placental and uterine tissue will be analyzed. Antiserum to porcine RXN and goat antirabbit IgG-colloidal gold will be used to localize the antigen. Since oxytocin has been suggested to be an ovarian product, we will also use the above techniques to attempt to isolate and localize this hormone in rabbit tissue.